Tapping apparatus



NOV. 14, 1950 A, J, SCHAlD 2,530,268

TAPPING APPARATUS Filed Aug` 14, 1945 A xii-2:33

IN V EN TOR.

A TTORNEY Patented Nov. 14,- 1950 -Y UNirsoA. STAT TAPIIVNG APPARATUS Arthur J. SchaidChicago, Ill., assigner to Westl ern vElectric Company, Incorporated, New York, N. Y.,v a corporation of New York Applicaton'Al-lgustll, 1945, Serial No. 610,691 Y This invention relates to tapping apparatus and more particularly to a tapv for tapping rounded notches in slots or retapping previously threaded holes.

, It is an object of the-present invention to provide a tapping apparatus-for producing burr-free threads.

In accordance with one embodiment of the invention, a tap inadesimilar to astandard bottom tap, is ground at its entranceend in such lmanner that the tip or entrance end surface starts at the same helical angle as the first full thready and continues for a complete revolution around the tip ofthe tap, whereby, after the rst revolution, the first cutting edge or tooth cuts a full thread and forms a heavy chipv which -will not tend to adhere toV the threads.. The tap is mounted in a drive mechanism, which is responsiveto pressure inopposite directions .to

drive` the tap in a direction depending upon the direction that pressure is applied to the tap,

A completeunderstanding of the invention may be vhad by reference to the following detailed description when considered in conjunction with the accompanying drawing', wherein Figl is a front elevational View ofa tapping apparatus made in accordance with the present.

invention, parts being broken away to show details of the drive mechanism for the tap;

Fig. 2 is a greatly enlarged view of the entrance end surface of the tap;

Fig. 3 is a bottom plan View showing the entrance end surface of the tap; and

Fig. 4 is a fragmentary detail view of a part which may be readily threaded by using the tap shown in the other figures.V l

In the drawings, the tapping apparatusis shown lr'nrovided-w-ith an upper housing I0, from which there extends a drive shaft II carrying a pulley I2, which may be driven from anysuitable power source, not shown. The drivel shaft I I is splined to a shaft I3, thus to rotate the shaft lwhen the shaft Il is driven, butto permit relative reciprocation between the4 shafts `II and I3. A lower housing' t4, havinga'cylindrical projection I5 thereon, is slidable with respect to the upper housing I0 and is fixed against rotation with respect thereto. Any suitable means may be provided for imparting reciprocation to the lower housing I4, for example, a pneumatic control device, illustrated diagrammatically at I6.

The lower housing I4 includes a casing I1, in which suitable gearing is provided for imparting rotation to a tap I8. Attached to the lower end of the splined shaft I3 is an upper driving clutch 3, claims'. (o1. iii-141) member I9, which is journalled in a bearing 20' set into the lower housing I4. The upper driving clutchmember has a gear 2'I cut intoL itsl periphery toV mesh with a gear 22 rotatable on a fixed shaft 23 which is, in turn, mounted within the casing Il! oi the housing I4. The gear Z-Zis attached to a sleeve 24, which, in turn, nasa gear 25 fixed toits lower end in position to mesh with anintermediate gear 25 mounted on a stu-d shaft 2l. Meshing with theintermediate gear 2-1 is a gear 23', which is fixed to a lower driving clutch member 20.

The upper and lower driving clutchmembers are of substantially the same construction and haveopposed internal facesv positioned to be engaged by a double cone driven clutchA member 40, which is leyedto a tap driving shaft 4I by means of a pin d2. The shaft 4I has its upper end ro`V tatably mounted in a bearing 43 set into the upper dri-ving clutch member and is freely ro tatable in a sleeve 44 formed integrally with the lower driving clutch member which is, in turn, rotatably mounted in a bearing 45A set intothe casing Il. A shouldered collar 4'6- surrounds the tap driving shaft 4I and is rotatable in a bearing 41' set into the lower end of the casing I'I. The-collar dfiY serves to support a compression spring 48, which surrounds a reduced portion of the tap driving shaft, and serves to resiliently hold the tap driving shaft 4I in the position shown. in Fig. 1, where the driven` clutch mem-A ber d'0 will be out of engagement with the driving clutch` members I9 and 29.

The weight of the tap driving shaft 4I, driven clutch member 4d and chuck 49.l which holdsthe tap. I8' on the shaft 4I, are sufficient to hold the driven clutch member out of engagement with the driving clutch member I9 and the spring 48 is sufficiently strong toy hold the driven clutch member 4&3y out. of engagement with the driving clutch member 2e. However, when: the tap Ii is moved downwardly under control of the pneumatic-control device I6' to engage the end of the tap with an article 5.0, the tap |81, on engaging the article', wil-l1 resist downward. movement and, as the lower housing I4 continuesto-move downwardly, the driving clutch member I9 will engage with the driven clutch member 40 to drive the tap in a direction to cut a thread 5I in the rounded notches 52 at the sides of the slot 53 formed in the article 50.` The article may be supported on any suitable base 54.

As soon as the thread 5I is tapped in the sides of the slot 53, the pneumatic control device I6 may be operated to cause the lower housing I4 to move upwardly. As soon as the housing I4 starts to move upwardly, the driven clutch member 40 will be disengaged from the upper driving clutch member I9 and continued movement upwardly of the housing I4 will cause the clutching faces of the lower driving clutch member 29 and driven clutch member 40 to engage and reverse the direction of rotation of the tap I8 until the tap is disengaged from the slot which it has threaded, at which time the spring 48 will restore the driven clutch member 40 to its middle position, as shown in Fig. 1, to stop further rotation of the tap due to the unclutching of the driven clutch member from both of the driving clutch members. The gearing extending from the gear 2| through gears 22, 25, 26 and 28 is such that engagement of the driven clutch member 49 with the upper driving clutch member causes the tapto be rotated in one direction, Whereas the engagement of the driven clutch member t with the lower clutch member 29 causes the tap to be rotated in the opposite direction.

From the foregoing, it will be seen that the tap I8 is resiliently engaged with the article to be tapped and that the clutching of the tap to its actuator must result in some slight slippage at the beginning of the clutching of the two clutch members one to another. This will permit the tap to be rotated slightly under either the urging of gravity or the spring 48 so that the tap will be permitted to drop into the slot 53 before it starts to cut. This is necessary since the entrance end of the tap and the first cutting tooth of the tap will, in the first complete revolution of the tap after it is dropped into the slot 53, cut one complete thread.

By referring to Figs. 2 and 3, it will be seen that the tap I8 has oppositely disposed utes B0 and I formed in it, between which are lands 62 and 63.- The entrance end surface 64 of the tap has everywhere at radial sections an angle equal to the thread angle and recedes axially away from said end on a helix equal to the thread helix angle, thus providing a generally coned surface with its apex eccentric to the tap axis and this surface is a continuation of the first thread adjacent thereto. The entrance end surface 64 of the tap thus consists of a prolongation of the rst thread and, since the thread is helically formed at the tip of the tap, the extension or pro-y longation 0f the thread surface merges to form an `irregular surface, the extreme tip end of which is eccentric with respect to the longitudinal axis of the tap and comprises a curved edge. In tapping Operations, the farthest extending portion of the ta-p will thus engage with the edge of the slot 53 t0 be tapped and will hold the threads out of cutting relation with the material of the article to be tapped until the utes B0 and BI are substantially parallel to the edges of the slot, thus to permit the entrance end surface S4 of the tap to drop into the slot and begin cutting the thread. Accordingly, when resiliently engaged with the surface of a part at the edge of the hole to be tapped, the tap I8 will not cut the part until it has dropped into the slot 53 and will then,

in the first full revolution, cut a thread to the full depth of the major diameter of the tap. Obviously, this first thread cut in the part will not -be complete, in that it will not include the full thread angle, due to the engagement of the entrance end surface 64 of the tap at the point diametrically opposed to the cutting face with the edge of the notch 52. However, after the first revolution, the tap will cut a full thread in each revolution thereof.

What is claimed is:

1. A screw thread-cutting tool comprising a tap having its entrance end defined by a surface having everywhere at radial sections an angle equal to the thread angle and receding axially away from said end and on a helix equal to the thread helix angle providing a generally coned surface with its apex eccentric to the tap axis and this surface being a continuation of the first thread adjacent thereto, and having the first thread-cutting surface extending to the major diameter of the tap thread to cut a full thread for each complete revolution following the first revolution.

2. A screw thread-cutting tap for retapping or tapping opposed edges of slots having longitudinally extending flutes defining lands and an entrance end defined by a surface having everywhere at radial sections an angle equal to the thread angle and receding axially away from said end and on a helix equal to the thread helix angle providing a generally coned surface with its apex eccentric to the tap axis and this surface being a continuation of the first thread adjacent thereto, and a thread-cutting tooth formed at the entrance end of said tap to conform to the maximum major and minor diameter of the tap.

3. A luted screw thread-cutting tap for tapping opposed notched edges of slots in articles having its entrance end dened by a surface having everywhere at radial sections an angle equal to the thread angle and receding axially away from said end and on a helix equal to the thread helix angle providing a generally coned surface with its apex eccentric to the tap axis and this surface being a continuation of the first thread adjacent thereto.

ARTHUR J. SCHAID.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Dec. 11, 1874 

